Removal of impurities from liquids by contact with dolomitic lime calcined for 10 to120 minutes at a temperature of 300 u deg. c. to 700 u deg. c., and product therefor



June 1, 1948. c CALMQN 2,442,584

REMOVAL OF IMPURITIES FROM LIQUIDS BY CONTACT WITH DOLOMITIC LIME cALcIEED FOR 10 T0 120 MINUTES AT A TEMPERATURE OF 500 0. TO 900 0. AND PRODUCT THEREFOR Filed July 7, 1942 SILICA REMOVAL AT ROOM TEMPERATURE WITH PROCESSED DOLOMITIC LIME la Z 5 W 2.0

Q- E z 0.

o F R 2 as a 2 '2 z n. 3

PERIOD OF CALCINATION m mmu'rcs AT 500 c.

m SILICA REMOVAL TESTS WITH SLUDGE .2 z u ACCUMULATED FROM RUN TO RUN 3 O 3 2 3.0 I r PROCESSED DOLOMITIC LIME 2 E/ 0 I I 2.5 U z 5 & c: .f 2 Z Z if 9 *--J o 5 0 g I E m 3 Z 9: i 5 COMMERCIAL DOLOMITIC LIME 2 3 o 1.0 2 U 1 2 t 2 1 a z 05 g 9 E o 5 D Z INVENTOR 5 l0 CALVIN CALMON NUMBER OF RUNS BYM K ATTO R N EY Patented June I, 1948 REMOVAL 8 FROM LIQUIDS BY OONTAC'I' wrm OALCINBD FOR 10 T0 TUBE OF 880' 0. T0 N0 0., AND

TEMPE PRODUCT DOLOMITIC LIME 120 MINUTES AT A Calvin Calmon, Mount Holly, N. 1., auignor to The Permntlt Company, New York, N. Y., a corporation of Delaware Application July I, 1942, Serial No. 450,088

3 Claims. (CL 210-23) This invention relates to the removal oi impurities from materials requiring treatment with lime by the use of flnely divided dolomitic materials containing magnesium compounds oi high absorptive capacity, to dolomitic materials suitable i'or this purpose, and to the preparation of such highly absorptive materials.

The me of magnesium compounds for removing dissolved impurities such as silica and fluoride from water has been developed to the point where such processes are commercially practical. The general principles which govern the use of magnesium compounds for the removal of silica are described in a paper entitled Silica removal by an improved magnesia process, by Howard L. Tiger, published in Journal of the A. S. M. E. in vol. 64, No. 1, pages 49-63, January. 1942. D010- mitic lime has been used successfully in this connection to remove silica and fluoride from hard water, and has the dual function of soitening the water simultaneously with the removal 0! the dissolved impurities.

I have found that relatively inexpensive dolomitic materials containing um compounds can be treated in such a manner as to increase substantially their ability or capacity for absorbing impurities, such as silica, fluoride and other materials. While ordinary dolomitic limes obtained on the market can be used with good results, the eflectiveness of such a material can be increased several times by a treatment consisting essentially oi calcining or heat treating the double hydrated product to drive ofl a. portion of the moisture in it. Such a specially prepared dolomitic lime is unusually efiective for absorbing impurities in chemical processes that require the use of lime.

One object 0! this invention, therefore. is to utilize a highly absorptive dolomitic lime for absorbing impurities in a process which normally requires the use of lime.

Another object of this invention is the provision of an improved process for removing dissolved impurities such as silica or fluoride from water by treating the water with a dolomitic material containing highly absorptive magnesium compounds.

A further object of the invention is the provision oi specially prepared dolomitic materials that are much more effective than ordinary dolomitic materials for absorbing impurities.

A further object is the provision 01' a method 01' preparing dolomitic materials suitable for the foregoing purposes and containing magnesium compounds in a highly absorptive form.

The invention will be described in conjunction with two graphs shown in the accompanying drawings. in which Figure l is a graph showing the effect of difl'erent calcining periods at 500' C. upon the silica absorbing ability of double hydrated dolomitic lime.

Figure 2 is a graph comparing the abilities of a specially treated dolomitic lime and an ordinary dolomitic lime to remove silica from water during a number 01' successive runs.

Ordinary dolomite is usually regarded as the double carbonate 0! calcium and magnesium, and while dolomites vary over a. considerable range in their respective proportions oi calcium and magnesium. the common form of dolomite is generally expressed chemically as CaC'Os-MgCOa. Ordinary dolomite is usually converted to dolomitic lime by calcining at a temperature high enough to decompose both the calcium carbonate and the magnesium carbonate. thus leaving a product which is regarded as the double oxide of calcium and um and may be expressed as CaO'MgO. when dolomitic lime ls hydrated by simply placing the dead burned lime in water, the hydrate formed is represented by the formula Ca (OHla-MgO. when steam is used to hydrate the dolomitic lime. both the calcium and magnesium oxides are converted to the corresponding hydroxides, so that the double hydrated product may then be expressed as comma-Maori Dolomitic lime is regarded as fully hydrated when approximately 01 the magnesia becomes hydrated.

I have found that'the applications! a controlled heat treatment to a double hydrated dolomitic lime greatly increases the ability of the product to remove impurities such as silica or fluoride from water treated with the resulting product. 01 course. ii too high a. heat treating tempertaure is employed tor too long a time, the material will be converted back to its original condition 01' substantially dead burned dolomitic lime. By using lower temperatures or shorter heat treatments, however, so that the heat treatment is stopped short oi converting the hydrated dolomitic lime back to its original dead burned condition, I have found that the absorptive ability or capacity oi the material is greatly increased. For most purposes. a calcining temperature of the order or 300 to C. is well suited for this treatment. The time of calcination can be varied over a considerable range, but optimum results require a proper correlation of the temperature and time 01 treatment.

For example. when double hydrated dolomitic lime is calcined at 500 0.. a product with the best silica and fluoride removing properties is obtained by a heating period lasting about minutes. At lower temperatures. oi course. somewhat longer heating times are necessary to produce comparable results. and at higher temperatures than 500 C. excellent results may be obtained with heating periods oi less than 15 minutes.

Furthermore, longer times oi heating at 500 0., or higher temperatures will produce excellent products. At 500 0., heating periods oi minutes, minutes or even two hours produce products which are many times more eflective in removing silica or fluoride irom water than either ordinary dead burned, simple hydrated or fully hydrated dolomitic lime.

The eflect 01' these diiierent periods oi heating is illustrated by the graph in Fig. 1. In this graph, the amount oi silica absorbed is plotted as the ordinate against the time oi heating of double hydrated dolomitic lime at 500 C. The fully hydrated dolomltic lime and the products calcined at 500 C. for 10, i5, 30, 60 and 120 minutes were each tested for their silica absorbing ability by esitating a given weight oi the product with a given volume or raw water containing 4.6 P. P. M. oi silica. In each case. the agitation was continued for one hour. and the treated.

water was analyzed for silica after a one half hour settling period. The marked superiority oi the products after calcinaticn is clearly apparent.

In Fig. 2, the cumulative eflect of a calcined double hydrated dolomitic lime is compared with the cumulative eiiect oi a commercial dolomitic lime in removing silica irom water. In this graph, the silica removing capacities of the prodnets are plotted as ordinates against the number of runs as abscissae. The data for these curves were obtained by agitating successive portions of raw hard water containing 15.4 P. P. M. 01' silica with given quantities oi the product in question. The sludge iormed was allowed to accumulate irom one batch of water to the next, and the treated water irom each batch was analyzed for silica. Curve Number 1 was obtained by following this procedure using commercial dolomitic lime. and curve Number 2 was obtained by using a double hydrated dolomitic lime that has been heated at 500 C. for 15 minutes.

The absorptive capacity oi such calcined hydrated materials ior removing fluoride from water is similarly much greater than the capacities of the iully hydrated or dead burned materials. Tests on water containing 5.2 P. P. M. of fluoride have shown that calcined double hydrated dolomitic lime calculated in this manner reduces this fluoride concentration to 1.0 P. P. M., whereas rdinary dolomitlc lime used under the same conditions only lowers the fluoride content to 2.5

P. P. M, a quantity which is still high enough to render the water unhealthy for human consumption.

During the heating or calcination oi the canon) r-Mg(0H) a, the material loses weight due first to the decomposition of the MgiOI-I): into MgO and H20. The Ca(OI-I)a does not appear L0 decompose into CaO and H10 to any great extent until after the MgiOH): has been substantially completely changed into MgO.

While better results are probably obtained by stopping the heating or calcining treatment before all oi the MsiOH): has been dehydrated,

4 good results are also obtained it the heat treatment is carried to the point oi dehydrating all'oi the magnesium hydroxide and a portion oi the calcium hydroxide.

My new dolomitic materials are particularly useiul ior removing dissolved impurities from aqueous liquids, as in the treatment oi hard water where the lime operates to precipitate hardness constituents irom the water and the highly absorptive magnesium oxide absorbs large amounts or impurities such as silica or fluoride dissolved in the water.

Examples of other processes in which these specially prepared dolomitic materials may be used to advantage include the flnal clarification step in the purification of gelatin and glues. Ii this is the case, the alum or phosphoric acid in solution would be coagulated by the lime in thecalcined double hydrated dolomitic lime and the magnesium compounds would reduce the amount of impurities in the final product.

Also in the leather tanning industry,-these new dolomitic limes may be used to lime the animal hides and reduce the frequency oi preparing fresh lime baths because oi the absorption of organic decomposition products and other impurities.

In the purification oi sugar Juices normally treated with ordinary lime. the substitution of my improved dolomitic lime may be used to assist in the removal of impurities from the sugar solution simultaneously with precipitation of the lime. thus facilitating and possibly even eliminating some of the subsequent purifying steps of the process.

In fact. these new dolomitic materials have been described particularly in connection with removal of silica and fluoride irom water, but they may be used generally in the treatment oi aqueous liquids where the lime is used up in some manner and the magnesium compounds serve the useful function oi absorbing various impurities.

By the term "dissolved" impurities such as silica or fluoride is meant those impurities that are in true solution or are dispersed in the liquid in substantially colloidal form. as distinguished from salts in suspension.

The terms and expressions which I have employed are used as terms of description and not of limitation, and I have no intention. in the use of such terms and expressions, oi excluding any equivalents of the features shown and described or portions thereof. but recognize that variousmodifications are possible within the scope oi the invention claimed.

I claim:

1. A process of removing dissolved impurities selected from the class consisting oi silica and fluorides from aqueous liquids comprising adding to the liquid a double hydrated dolomitlc lime calcined for about 10 to minutes at a temperature of about 300 to 700 C. and thereafter separating the liquid from solid matter mixed therewith.

2. A composition for removing dissolved impurities selected from the class consisting of silica and fluorides from an aqueous liquid said composition comprising double hydrated dolomitic lime calcined for about 10 to 120 minutes at a temperature of about 300 to 700 C.

3. A process of increasing the ability of dolomitic materials to remove impurities selected from the class consisting of silica and fluorides from aqueous liquids, said process comprising heating a double hydrated dolomitic lime for about 10 to 120 minutes at a temperature of about 300 to 700 C.

CALVIN CALMON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 283,472 Dudley Aug. 21, 1883 705,253 Krause July 22, 1902 773,395 Jones Oct. 25, 1904 1,315,836 Hoffman Sept. 9, 1919 1 1,604,126 Kern Oct. 26, 1926 1,653,272 Green et al Dec. 20, 1927 Number Name Date 2,207,725 Elvove July 16, 1940 2,317,961 Tschirner Apr. 27, 1943 FOREIGN PATENTS Number Country Date 3,730 Great Britain 1886 100,590 Sweden Nov. 7, 1940 OTHER REFERENCES "Industrial and Engineering Chemistry, June, 1941, pages 817-818 cited, article entitled Dolomitlc Lime, a copy of which may be found in 210-23.

Mechanical Engineering (January 1941), pages 34-35, article entitled Silica Removal." 

